1. Field
Exemplary embodiments relate to an electrical energy storage device and manufacturing method thereof, and more particularly, to an electrical energy storage device with improved connection structure between an outer terminal and an inner terminal and manufacturing method thereof.
2. Description of the Related Art
Generally, an ultracapacitor, also known as a supercapacitor, is an energy storage device having characteristics in between those of an electrolytic condenser and a secondary battery. Since an ultracapacitor has high efficiency and a semipermanent life span, the ultracapacitor is considered as a next-generation energy storage device that is useable in parallel with or in replace of a secondary battery.
An ultracapacitor can also be used to replace a storage battery in applications that are not easy to maintain and that require a long service life. Since an ultracapcitor has quick charging/discharging characteristics, the ultracapacitor is very suitable as a main or auxiliary power supply of electric vehicles, road indicator lamps, or uninterrupted power supplies (UPSs) that requires high capacity, as well as an auxiliary power supply of mobile communication information equipment such as mobile phones, laptop computers, or personal digital assistants (PDAs), and thus has been widely being used as the same.
As shown in FIG. 1, an ultracapacitor mainly has a cylindrical shape for minimization.
Referring to FIG. 1, a cylindrical ultracapacitor includes an internal housing 10 that accommodates a bare cell composed of a cathode, an anode, a separator, and an electrolyte, a metallic casing 40 that receives the internal housing 10, inner terminals 20 and 30 located at the upper and lower portions of the metallic casing 40 to connect to the anode and the cathode of the bare cell, respectively, and an outer anode terminal 51 and an outer cathode terminal 45 located at the top and bottom of the metallic casing 40, respectively.
In the cylindrical ultracapacitor, the inner anode terminal 20 is electrically isolated from the metallic casing 40 by an insulating member 60 and electrically connected to the outer anode terminal 51 located in the middle of a plate-like member 50, and the inner cathode terminal 30 is electrically connected to the metallic casing 40.
Conventionally, the connections between the inner anode terminal 20 and the plate-like member 50, and between the inner cathode terminal 30 and the metallic casing 40 are made using a bolt 70. However, a connection between an inner terminal and an outer terminal using the bolt 70 has disadvantages of a complicated assembly process and low connection stability.
Particularly, since the outer anode terminal 51 is formed with an electrolyte injection hole at the center thereof and has components such as a safety valve and the like, it is not easy to apply a bolt to the outer anode terminal 51.
To solve this problem, suggestion has been made to weld, using a hot compress, the surface of the plate-like member 50 provided with the outer anode terminal 51 and the corresponding surface of the inner anode terminal 20. However, this involves a complicated welding process, and since the connected part between the outer anode terminal 51 and the inner anode terminal 20 is weak against the external vibration, the outer anode terminal 51 and the inner anode terminal 20 may easily separate from each other, which will deteriorate the contact resistance characteristics.
On the other hand, since the inner cathode terminal 30 directly contacts the metallic casing 40, it is very important to minimize the contact resistance between the inner cathode terminal 30 and the metallic casing 40 and stabilize the contact state therebetween to improve the electrical characteristics of the ultracapacitor.
Meanwhile, a side reaction may occur at the interference between the electrolyte and the electrode of the ultracapacitor at room temperature under abnormal conditions such as overcharge, overdischarge, overvoltage, and the like, and as a result, gas is generated. When gas accumulates in the ultracapacitor, the internal pressure of the metallic casing 40 increases and finally swells the metallic casing 40. In some cases, when gas abruptly discharges through a weak area of the metallic casing 40, the metallic casing 40 may explode.
In particular, the metallic casing 40 swells more severely at the side and the bottom of the metallic casing 40 near the inner cathode terminal 30 than in the vicinity of the inner anode terminal 20.
Since the metallic casing 40 has a curled portion 41 formed on the top thereof near the inner anode terminal 20, it is easy to reinforce the pressure resistance performance of the side of the metallic casing 40 near the inner anode terminal 20 by controlling an amount of curling, however since a curled portion is not formed in the vicinity of the outer cathode terminal 45, it is not easy to reinforce the pressure resistance performance of the side of the metallic casing 40 near the outer cathode terminal 45.